1. Field of the Invention
The present invention pertains to a cylinder and piston type device for making measurements of vapor pressure of liquid compositions, together with a method of making such measurements of true vapor pressure of a multi-component liquid composition, in particular.
2. Background
U.S. Pat. No. 4,783,989, assigned to the assignee of the present invention, describes a vapor pressure measurement system having a cylinder member in which a reciprocable piston is disposed for movement to contain a sample of liquid and to expand a chamber formed by the cylinder and piston while measuring the pressure in the chamber until a pressure is obtained indicative of the vapor pressure of the liquid. In the further development of a system along the lines of that described in the abovementioned patent, it has been determined that improvements in the fluid inlet and outlet flow paths and valving was required and that the relationship of the surface area of liquid to the depth of liquid in the chamber should be increased to reduce the liquid path length through which vapor bubbles are required to travel in order for an equilibrium condition of vapor and liquid to be reached in a reasonable period of time. This is particularly important for multi-component liquids such as crude oil and refined petroleum liquids.
Still further, in order to improve the accuracy of measurement of vapor pressure in a device generally of the type described in the above-referenced patent, and to reduce the time required to take measurements, it has been determined that an improved methodology was necessary. Briefly, at least two measurement points were deemed necessary to establish an accurate estimation of the true vapor pressure, and the time required to make the measurements should be reduced so that the apparatus can be used on a continuous basis to make measurements of process and transport flowstreams. It is to these ends that the present invention was developed with a view to providing an improved vapor pressure analyzer and method of estimating true vapor pressure of various liquids, particularly multi-component liquids such as crude oil and refined petroleum products.